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A number of methods for the regeneration of aldehydes and ketones from their 2,4-dinitrophenylhydrazones have been suggested and their usefulness and limitations discussed.1-14 In all of these regeneration methods the 2,4-dinitrophenylhydrazone is heated with an acid, usually a keto acid. Little, if any, attention appears to have been given to the possibility of a base-catalysed regeneration. An investigation made of the stability of the 2,4-dinitrophenylhydrazones of octanal, heptanal, citronellal, and octan-2-one to heating in aqueous ethylene glycol in the presence of potassium bicarbonate has shown that one of the products of the reaction is a steam-volatile oil which appears to consist almost completely of the corresponding carbonyl compound. The yield is about 60% for the aldehydes and 35% for the ketone. The identifications have been based mainly on gas chromatography on polar and non-polar stationary phases, though thin-layer chromatograms of the derived 2,4-dinitrophenylhydrazones and their mixed melting points have provided confirmation. Each of the carbonyl compounds distils from the reaction mixture with a small amount of a coloured compound which is not soluble in dilute acid or alkali but can be eliminated by distillation of the oil, either alone or with steam. For octane-2-one and citronellal, thin-layer chromatograms suggest that the coloration is due to the presence of the corresponding 2,4-dinitrophenylhydrazone. Presumably in the other cases also a small amount of the 2,4-dinitrophenylhydrazone distils or is formed from some 2,4-dinitrophenylhydrazine which has distilled. The regeneration occurs at comparable rates for the three aldehydes studied, but is much slower for the ketone under the same conditions. If the proportion of

The base-catalysed regeneration of some carbonyl compounds from their 2,4-dinitrophenylhydrazones